More than 20,000 people are expected to attend the event, including Prince Charles and the Duchess of Cornwall.

A colourful sprawl of marquees, gardens and stalls fills the rolling parklands of the Royal Estate, for a day-long celebration of gardening and outdoor living.

Volunteers have worked all year to bring the show together. They are proud of both its Royal traditions, which date back 150 years and the tens of thousands each event raises for a raft of charities and good causes.

Show chairman David Reeve said: 'If it goes like the build up it will be the best ever. It doesn't just happen on the Wednesday, those show gardeners have been working since last Thursday. Those gardens don't just happen, it's a massive effort.'

Mr Reeve said the garden in the Royal Marquee, sponsored by Adnams Brewery and Notcutts, in association with the show's media partner the EDP, was 'exceptional'.

Sumptuous planting, including a 30ft birch tree, recreates a pub garden decked out in celebration of the Queen's 90th birthday. Designer Marco De Jongh, building his first garden at Sandringham, said bringing the display to life in a marquee had been a challenge.

'The people from the estate have been so friendly,' he said. 'They can't do enough for you, it's fantastic. I think we might be back next year, it's brilliant.'

Show gardens include the Villa Via Silva - a mock Roman villa inspired by archaeological finds at Woodgate Nursery, near Aylsham. Catherine Mullenger, volunteer co-ordinator with the Aylsham Roman Project, said a geophysical survey of the nursery had shown a villa had once stood on its kitchen garden, with pottery kilns in a nearby field.

Show regular John Shone has designed a garden celebration the 85th anniversary of the King's Lynn and District Branch of Guide Dogs for the Blind. Built by Farm and Garden Ltd and Rutland Willows, it features sensory plantings around a willow statue of a partially-sighted person with their guide dog.

Gill Southgate, chair of the branch, visited with her guide dog Jazmine. She said: 'There's so many different features it's brilliant. It's a lovely sensory garden.'

Next door Shadow Hall, from Smallborough-based Hall Landscaping and Design, has built Half Wild to show how gardeners can have the best of both worlds.

'It's about having a garden that looks like a garden, with a wild area as well,' she said.

Ralph and Linda Nichols designed Loved, Lost and Found to evoke a person's journey through dementia.

'When a person has dementia, life and a garden can become lost, chaotic and less-ordered, although the meaning, purpose, beauty and love remain,' she said.

Mrs Nichols said the display would not have been possible without the support of Graham McDonald, from North Walsham Garden Centre, who sponsored the plantings and helped to build it.

She added a collection would be made on the garden for Joy Instead - a charity which helps people with dementia stay living in their own homes.

Snettisham-based design and landscaping firm ABC has built a striking small garden with a shady purple arbour.

'It's to show what you can achieve in a typical small garden, said the firm's Susie Crook.

Friends Mary Bentley and Caroline Bishop's colourful garden was inspired by the Greek myth of Pygmalion - aka My Fair Lady. The pair propogated their own plants for the show.

Richard McCarraher's Aquaponics is the first show garden to be based on an ancient system where waste from a fish pond is used to generate fertiliser.

'The fish produce ammonia and various other things, which are pumped through the plants and the plants' roots absorb the nutrients and clean the water for the fish,' said Bunwell-based Mr McCarraher.

The garden has been created in conjunction with the charity Red Balloon, which supports young people who stay away from school because of bullying or other issues.